The invention relates to a method for eliminating squeaking noises occurring when operating a window lifter for motor vehicles which is driven by an electric motor.
Window lifters of this kind may entail the problem, especially after some time in service, of giving rise to squeaking noises, which are highly disturbing to drivers and possibly passengers, when vehicle windows are opened and/or closed. The causes of the squeaking noises are known. They result from vibrations which are produced by sliding movements of the drivers for the window glass on guide rails. The characteristics of the squeaking noises with regard to frequency band and noise level vary from vehicle to vehicle and have to be determined when developing the vehicle, without there being any success in reliably eliminating the noises through purely constructional measures.
The object of the invention is to provide a method by means of which squeaking noises of this kind can be effectively eliminated.
According to the present invention, there is provided a method for eliminating squeaking noises occurring when operating a window lifter for motor vehicles, the window lifter being driven by an electric motor, wherein the squeaking noises are detected by a system for evaluating acoustic signals which generates for the duration of the squeaking noise a command signal which is delivered to a window lifter control device which varies the speed of the electric motor within fixed limits, until the system for evaluating acoustic signals no longer detects any squeaking noise or it is recognised that speed variations are ineffective.
This method is based on the finding that the squeaking noises occurring when operating window lifters are dependent on the speed at which the drivers slide on the guide rails.
It is preferable to use, as an option, a voice control system provided in the motor vehicle as a system for evaluating acoustic signals. In this case it is assumed that voice control systems (car telephone, telematics, etc.) are already and will in future be provided with increasing frequency in the vehicle. A voice control system of this kind is equipped with a microphone and evaluates the acoustic signals in the vehicle interior. On the basis of the characteristics (frequency band and noise level) of a window lifter squeaking noise which are determined at the development stage, a voice control system is able to recognise an occurring noise as a window lifter squeaking noise.
If the noise is detected as a window lifter squeaking noise, the command signal which is thereupon generated can advantageously be delivered to the window lifter control device via a CAN (controller area network), if this is provided. In this case the information that a window lifter is squeaking is relayed by means of the added-feature CAN to all nodes of the CAN network.
The speed variation of the electric motor expediently takes place by means of pulse width modulation (PWM) signals. This opens up the advantageous possibility of storing the pulse width modulation state which exists upon cessation of the squeaking noise and the position of the vehicle window at the time, and of retrieving this pulse width modulation state from the memory each time the vehicle window passes through this position in order to control the speed of the electric motor accordingly.
The variation in the speed of the electric motor within the fixed limits preferably takes place stepwise.